A novel measurement approach based on optical coherence tomography for inline quality assessment of thermoplastic glass-fiber reinforced unidirectional tapes

Optical coherence tomography (OCT) has been found to be a powerful method for nondestructive testing of glass-fiber reinforced polymeric composites. Various authors have investigated the use of OCT in offline lab-scale detection of fiber orientation and defects in thermoset-based composites. This work evaluated the potential of OCT as a technique for detecting common defects in the continuous production of thermoplastic glass-fiber reinforced unidirectional (UD) tapes. Measurements were first conducted with a stationary OCT sensor using a spectral domain system to investigate: (1) insufficiently impregnated fiber regions, (2) unfilled gaps, (3) polymer accumulations causing fiber/matrix irregularities, and (4) rough tape surfaces. Optical microscopic analysis was used for validation. To overcome the limited maximum field of view of modern OCT setups, we then developed a novel inline test rig to accurately simulate process conditions and measure across the whole tape width. We show that OCT is a reliable method for acquiring cross-section information on tape quality both at the lab scale with a stationary sensor and inline with a sensor moving across the tape surface. Our OCT measurements were in excellent agreement with our offline microscopic investigations. OCT is a powerful, non-destructive and high-resolution method for quality assessment of glassfiber reinforced UD tapes and has great potential for use in inline quality assurance systems.